Study on cooling process of decay heat removal systems in a reactor vessel of sodium-cooled fast reactor by scaled water experiments, 5; Transient behavior under operations of multiple decay heat removal systems

Aizawa, Kosuke ; Tsuji, Mitsuyo ; Kobayashi, Jun ; Kurihara, Akikazu ; Nakane, Shigeru*; Onuma, Hideyoshi*

Thermal-hydraulic phenomena driven by natural circulation in a reactor vessel was investigated by using scaled model water experiments simulating a reactor vessel to enforce the safety and to optimize the design and operation of decay heat removal systems under normal operation and severe accident conditions. This paper shows the results of transient behavior under operations of dipped-type DHX and penetrated-type DHX to clarify the effect of operating multiple decay heat removal systems on natural circulation phenomena in reactor vessel. From the experimental results, it was confirmed that the maximum temperature temporarily increased compared to the maximum temperature in natural circulation steady state by operating the second DHX after the natural circulation steady state was maintained under the first DHX operation.